Peter Krogh wrote:

> I replaced the pressure cap as the first diagnostic proceedure.  Even replace
> it twice.

Peter, give the thermostat a go. The thing may not be working properly. Could be
opening just the tinest bit enough to let some cooling to take place at low
speed, but when driving hard it's not enough, thus preventing adequate cooling
under heavier loads  resulting in possible boiling in the heads.

If you have access to one of those infrared heat sensing devices that some
mechanics use, you can, on an absolute cold engine start, monitor where the
heating is taking place in various parts of the engine, and also tell when the
thermostat begins to open. You can also get a relative reading on the themostat
by watching the changing reading on the meter as the various parts get hotter and
hotter as the engine continues warming up to normal operating temperature. The
sensors are great for trouble shooting. First developed by NASA to read rocket
engine and other component temps out on the launch pad, then addapted by the Auto
Racing world, and finally adapted to the average Auto shop.

Anyway, good luck.

John Rodgers
88 GL Driver